interFoam, high velocity's and decreasing timestep's

Kahnbein.Kai · August 22, 2021, 02:17

Hello,
i have a problem with my multiphase laminar simulation (Water, Air).

The simulations runs smooth, until water comes near the outlet (after 5-6 seconds), then the velocity's at the outlet rises up to 70-100 m/s and the timestep decreases to 10^-52.

I made a sketch (BouCon.jpeg) with the geometry and the assigned boundary location's, i also added a "will" flow path (flow.jpeg) of the waterphase.

The boundarys are:
green = atmo
blue = inlet
red = outlet
all others = walls

Here is my CheckMesh log:

Code:

Checking geometry...
    Overall domain bounding box (-11.513987 -10.740459 -0.35694548) (-6.65 -3.48344 0.8650929)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (1.5408662e-16 -1.7868697e-16 6.6448108e-16) OK.
    Max cell openness = 4.8142625e-16 OK.
    Max aspect ratio = 14.938371 OK.
    Minimum face area = 1.1015533e-07. Maximum face area = 0.00224492.  Face area magnitudes OK.
    Min volume = 1.4505393e-07. Max volume = 3.3031486e-05.  Total volume = 3.600383.  Cell volumes OK.
    Mesh non-orthogonality Max: 69.389349 average: 7.9464662
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 3.0778305 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

I testet my boundary conditions at the waterChannel template, there they will work flawlessly ...

Here are my U, p_rgh and alpha.water files:
U:

Code:

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    CAD_patch32 // atmo
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }
    
    CAD_patch39 // inlet
    {
        type            fixedValue;
        value           uniform (0 0 0.2);
    }
    
    CAD_patch0 // outlet
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }
    
      wall
    {
        type            noSlip;
    }
}
}

p_rgh:

Code:

dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
  CAD_patch32 // atmo
    {
        type            totalPressure;
        p0              uniform 0;
    }

    CAD_patch39 // inlet
    {
        type            fixedFluxPressure;
        value           uniform 0;
    }
    
    CAD_patch0 // outlet
    {
        type            fixedValue;
        value           uniform 0;
    }

      wall
    {
        type            fixedFluxPressure;
        value         uniform 0;
    }
}

alpha.water:

Code:

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;


boundaryField
{

    CAD_patch32 // atmo
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }
    
    CAD_patch39 // inlet
    {
        type            fixedValue;
        value           uniform 1;
    }
    
    CAD_patch0 // outlet
    {
        type            zeroGradient;
    }
    
     wall
    {
        type            zeroGradient;
    }
  }

I also added my fvScheme and fvSolutions files.

Have anyone a idea or a suggestions why my simulation is crashing ?

Best regards
Kai

edit: Sorry, my mixed the U and the alpha.water file up, now the correct files are displayed.